This application relates to methods and systems for customized cornea ablation in photo-refractive surgery.
Laser ablation can be used to remove small portions of the cornea in an eye to form a desired surface shape to improve the vision. A custom-ablation photo-refractive surgery, for example, can control a surgical laser beam by using measurements of the topographical profile of the cornea or the wavefront aberration of the eye to generate a customized ablation profile with high surgical accuracy. Such technique can be used to generate fine customized corneal profile to correct low-order refractive errors such as defocusing and astigmatism and high-order refractive errors such as coma and spherical aberrations. In comparison, conventional photo-refractive surgeries correct only the lower-order errors and may induce extra amount of high-order errors and lead to imperfections such as halo and night vision.
A widely-used laser source for the above custom-ablation photo-refractive surgery is an excimer gas laser. The output laser beam is focused onto the cornea and is scanned by a computer-controlled scanner.
The techniques and systems of this application are based in part on the recognition of special needs for the custom ablation in photo-refractive surgery and in part on the recognition of certain intrinsic limitations of typical excimer lasers for the accuracy re application. For example, it is desirable in the custom-ablation procedure to precisely control the laser energy deposition on the cornea with a fast and accurate compensation for the eye movement. A laser surgical system for the custom-ablation photo-refractive surgery is proposed herein to use a solid-state laser to produce a high pulse rate and near diffraction-limited laser beam to meet the special needs of the custom ablation in photo-refractive surgery.
In one embodiment, the solid-state laser is optically pumped by a continuous-wave diode laser to produce laser pulses, and a frequency-conversion element is used to convert the laser frequency in the deep UV range near 210 nm. The pulse repetition rate is about 500 to 1200 Hz. The output pulse energy of each pulsexe2x80x94is about 0.25 to 0.08 mJ. The spot size of the laser beam is focused to about 0.3 to 0.6 mm on the cornea, and is 3 mm or smaller on the scanner mirror. The pulse duration is 10 ns or shorter. The pulse to pulse fluctuation of this laser source is smaller than 10%, and the quality of the ablation beam is near diffraction limit (i.e. the M2 is 10 or smaller).
The fast scanner may include a pair of mirrors respectively engaged to two galvanometers and operate at a response frequency up to 1 kHz. Each of the galvanometer has a scanner mirror for a beam aperture of 5 mm or smaller. The near diffraction limited surgical laser beam enables the use of the small mirror and the fast operation of the scanner. The fast eye-tracking device may have a detection rate of kilohertz and can be coupled to the fast scanner. The near diffraction limited surgical laser beam enables the operation of the fast scanner and thus the operation of the fast eye tracker. The surgical laser system can then compensate the eye movement up to a kilohertz.
With a near diffraction-limited beam quality, this solid state laser allows for the use of the small scanner mirror for achieving fast scanning and engaging fast eye tracking.